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Re: Dinosaur diversity

 I see bursts of diversification, like those that produced
>the ceratopsids and hadrosaurs, but overall there seems to be a strange
>"sameness" about dinosaurian faunas for large periods of time.  

        A good point. Perhaps this effect is more apparent than real. We
only have a good record of dinosaurs from environments that favor
fossilization and preservation of large animals (with exceptions, like
Solnhofen etc.). The fossil record is not as forthcoming (with a few
exceptions) with dinosaurs (or any fossil, for that matter) from mountainous
regions, many forested areas, some (but far from all) deserts, and any other
place where >erosion< occured rather than >deposition< of sediments. Who can
know what wonderous beasts jumped from one rocky peak to another on the
Mesozoic mountaintops? How can we ever know what herbivores browsed in a
dry, savannah-like habitat? Only if there are streams or active dunes or a
depositing beach can we gain insight into the faunas of those times and places.
        Another problem is the bias towards preservation of big animals in
many high-energy environments where carcasses of small animals rapidly
disintegrate. Dinosaur Provincial Park is a good example. The really small
animals are there, but usually represented by isolated vertebrae, teeth, and
whatsuch. Perhaps animals analogous to Dixon's arbosaurs really did exist,
but any fossils of them would be so rare and so scattered and so isolated
that no complete picture of the animal could ever be formulated.
        There has been speculation that some pachycephalosaurs and
ceratopsians, known from rare and water-worn skulls, are allochanthonous
(deriving from elsewhere) inclusions in the faunas that they came to be
buried with. 
        A lot of dinosaur faunas should look the same because of their close
geographic proximity. An untrained eye would have difficulty distinguishing
a Lancian fauna from a Judthian fauna, but would have no problem telling the
difference between the faunas of North America and Europe of the Late
Cretaceous. As our knowledge improves of faunas that developed in isolated
areas, it is reasonable to expect an increase in diversity or at least
divergance from the ancestral stock will be observed.